They can be a money pit.
First is there any sign of water infiltration on the ceiling, walls, in closets etc? That can be a big problem. Check the roof for problems such as poorly caulked spots, tears in the roof anywhere water can infiltrate. If any spots then look in coach for a leakage sign
Tires if over 5-6 years old need to be replaced. This IS NOT dependent on the depth of the tire tread. Rv tires deteriorate from exposure to the sun and not being driven much. A blowout can cause thousands of dollars worth of damage. Tires can be expensive.
Spend some money and have a mechanic look over the vehicle portion to make sure mechanically sound
refrigerators can be a big money item so see the fridge operate on both A/C power and gas. Does the water heater work.
Belts, hoses etc can be deteriorated from age so they may need tending to, so nothing happens on the road.
You will most likely need new batteries to power the house portion. These will be about $150 each for 2, 6 volt batteries .